Solar cells which convert radiant energy from the sun into electrical energy are used to power spacecraft such as satellites. Designers of power systems for this application face numerous design constraints, of which weight is one of the most critical. The extraordinarily high cost of placing a pound of weight into space is a serious constraint, and any improvement which can reduce the weight and still provide adequate performance is actively sought.
Another constraint is the need for shielding the solar cells against radiation in regions of high fluence. An example is found in Van Allen belt radiation at about 7,000 kilometers height, which is where many satellites orbit. It is riot uncommon to apply a shielding layer of sufficient density to an entire craft merely in order to protect some parts of it, such as the solar cells. This significantly increases the weight of the craft. Any arrangement which can reduce the area or volume that must be shielded is also actively sought.
Yet another design constraint faced by the designer is the tendency of a concentrator-cell assembly to move out of proper alignment when bonded to a substrate which has a significantly different thermal coefficient of expansion. Additionally, the mechanical fatigue caused by this movement can degrade the system's lifetime.
Still another constraint is the volume required to pack a solar cell array into the spacecraft for containment while being launched. Reduction of stowed envelope volume is another design objective.
This invention provides an improvement for all of the above design constraints. It requires only a lesser area of cells for the same incident window area, and a configuration stowable in a lesser volume and readily deployable to a larger volume in which its elements are properly arranged. The lesser cell area requires less shielding. The consequence is a significant reduction of weight for the same kilowatt output, and a reduction of weight needed for shielding. A further consequence is that the reduced area of cells can reduce array costs. Also, the cells and their substrate can have a close match of thermal coefficient of expansion so as to eliminate movement of the cells out of alignment when the cells and substrate are heated, as they will be.